You can try to disable DNS over HTTPS. *https://support.mozilla.org/en-US/kb/firefox-dns-over-https *https://support.mozilla.org/en-US/kb/dns-over-https-doh-faqs You can check the connection settings. *Settings -> General -> Network: Connection -> Settings If you do not need to use a proxy to connect to internet then try to select "No Proxy" if "Use the system proxy settings" or one of the others do not work properly. See "Firefox connection settings": *https://support.mozilla.org/en-US/kb/websites-dont-load-troubleshoot-and-fix-errors *https://support.mozilla.org/en-US/kb/firefox-cant-load-websites-other-browsers-can *https://support.mozilla.org/en-US/kb/firefox-and-other-browsers-cant-load-websites See also: *https://appuals.com/pr-end-of-file-error/

As soon as I unchecked "Enable DNS over HTTPS" everything started working correctly again. That's really crappy of Mozilla to make a change like that without notifying everyone. While this was going on I tried a couple of other browsers and found one I like better. Thanks for your help though, it DID solve the problem.